Hi, Bob,

What temperature are you at when you give them the cold shower treatment.
Thermal cycling usually ramps at 5 degC/min, but such a cold dose from even
ambient could cause considerable thermal stress that crack any weak joints
you have, and maybe some good ones as well.

My question is, why plunge them into such cold? Are you beaming them out to
Pluto or some other place in the outer darkness?

Rgds

Pete Duncan





Bob Perkins <[log in to unmask]>@IPC.ORG> on 03/21/2001 06:09:44 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to Bob Perkins <[log in to unmask]>

Sent by:  TechNet <[log in to unmask]>


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cc:
Subject:  [TN] BGA Thermal Cycling and cold spray




Hi all,

I have a question regarding thermal cycling, a good pcb that has passed all
pretests and post tests with a typical thermal cycle.  A few PCBs were then
hit with a cold spray of -30c and then tested again, after this test a fall
out of 20%.  Are we introducing a crack by the severe thermal shock of the
cold spray or is it revealing a bad solder joint.

Thanks in advance,

Bob Perkins
SMT Process Manufacturing,
Automation Technician
Aimtronics-Delta

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